Reduction of copper (Cu) interconnect resistance is becoming an important issue for recent technology development. One of the promising approaches is to increase the Cu volume fraction by eliminating/reducing the physical liner thickness. Through barrier manganese silicate MnSiO3 formation has been proposed to address the technology challenge. See, for example, Usui et al., “Highly Reliable Copper Dual-Damascene Interconnects With Self-Formed MnSixOy Barrier Layer,” IEEE Transactions on Electron Devices, vol. 53, no. 10, pgs. 2492-2499 (October 2006) (hereinafter “Usui”).
However, the current integration scheme for forming the MnSiO3 barrier layer has many drawbacks. One notable drawback is that Mn from the barrier layer diffuses into the Cu interconnects. As an impurity, Mn that has diffused into the Cu interconnect undesirably increases the resistance in the interconnect.
Therefore, improved techniques for Cu interconnect fabrication would be desirable.